Arbuscular mycorrhizae: natural modulators of plant-nutrient relation and growth in stressful environments.

The human population is increasing by 0.96% annually and is estimated to reach from 7.3 to 9 billion in 2050 and 11 billion in 2100. The world's agriculture is under pressure to produce more food and ensure food security. On the other hand, around 40% of the cultivable land is already degraded due to various factors including urbanization, soil sealing, soil acidification, salinization, soil erosion, and contamination. Arbuscular mycorrhizal fungi (AMF) constitute a unique group of root obligate symbiont that exchange mutual benefits with about 90% of terrestrial plants and represents a key link between plants and soil mineral nutrients. Literature is scanty on the studies on massive inoculation of AMF in food crops in agronomic settings, and thereby achieving efficient uptake and minimization of the major soil nutrients, eventually meeting our food demand under increasing and inevitable stressed environments. Given above, this review aimed to (i) introduce agricultural soil-contamination, and the relation of soil microbiome with the health of soils and plants; (ii) briefly overview AMF; (iii) highlight AMF role as a bioinoculant, and enhancer of efficient uptake and loss-minimization of nutrients; (iv) appraise literature available on AMF role in the regulation of growth and nutrition mainly in vegetable, horticultural crops and fruit trees; (v) enlighten the role and major mechanisms underlying AMF-mediated regulation of plant growth and nutrition under major biotic and abiotic stresses; (vi) highlight AMF role in the minimization of greenhouse gas emissions; and (vii) list major aspects so far unexplored in the current context.

Characterization of partially purified alkaloids from Cucurbita maxima seed and evaluation of their antioxidant activity in human erythrocytes and leukocytes.

Cucurbita maxima, is a therapeutic plant spread all over the world. The seed of C. maxima constitutes a large amount of alkaloids, phenolic compounds, Vitamin E, and other secondary metabolites. The experiment was performed in four setups (Control, Only H2 O2 , H2 O2  + 25 mg of alkaloid, H2 O2  + 50 mg of alkaloids). The enzymatic and nonenzymatic antioxidants and lipid peroxidation (LPO) were determined to analyze the antioxidant effect of partially purified alkaloids. The results showed that partially purified alkaloids from C. maxima seed reacts effectively on the erythrocytes and leukocytes antioxidant enzyme system when compared to the hydrogen peroxide group. The present results indicate that the alkaloids present in this plant can be used as a natural antioxidant for the pharmacological purposes. PRACTICAL APPLICATIONS: The C. maxima seed constitutes rich source of alkaloids, phenolic compounds, Vitamin E, and other secondary metabolites. The results obtained revealed that the purified alkaloids from C. maxima seed acts as natural antioxidants, which enhanced the potential to scavenge H2 O2 and aids in protecting the RBC and WBC cells. The presence of 27 alkaloids of which seven major alkaloids possessing higher medicinal properties like antioxidant, antimicrobial, anti-inflammatory, antitumor, anti-aging, anti-diabetic, anticancer, anti-malarial, analgesic, nematicide, pesticide, and hemolytic activity were determined from the GC-MS analysis of the extract. Alkaloids acts as major constituent in phytotheraphy and has wide range of clinical application in humans and animals. In conclusion, alkaloids from C. maxima seed may have several properties that leading to the opening of new avenues in the natural product for the therapeutic purpose.

Catalase and ascorbate peroxidase-representative H2O2-detoxifying heme enzymes in plants.

Plants have to counteract unavoidable stress-caused anomalies such as oxidative stress to sustain their lives and serve heterotrophic organisms including humans. Among major enzymatic antioxidants, catalase (CAT; EC 1.11.1.6) and ascorbate peroxidase (APX; EC 1.11.1.11) are representative heme enzymes meant for metabolizing stress-provoked reactive oxygen species (ROS; such as H2O2) and controlling their potential impacts on cellular metabolism and functions. CAT mainly occurs in peroxisomes and catalyzes the dismutation reaction without requiring any reductant; whereas, APX has a higher affinity for H2O2 and utilizes ascorbate (AsA) as specific electron donor for the reduction of H2O2 into H2O in organelles including chloroplasts, cytosol, mitochondria, and peroxisomes. Literature is extensive on the glutathione-associated H2O2-metabolizing systems in plants. However, discussion is meager or scattered in the literature available on the biochemical and genomic characterization as well as techniques for the assays of CAT and APX and their modulation in plants under abiotic stresses. This paper aims (a) to introduce oxidative stress-causative factors and highlights their relationship with abiotic stresses in plants; (b) to overview structure, occurrence, and significance of CAT and APX in plants;

Jacks of metal/metalloid chelation trade in plants-an overview.

Varied environmental compartments including soils are being contaminated by a myriad toxic metal(loid)s (hereafter termed as "metal/s") mainly through anthropogenic activities. These metals may contaminate food chain and bring irreparable consequences in human. Plant-based approach (phytoremediation) stands second to none among bioremediation technologies meant for sustainable cleanup of soils/sites with metal-contamination. In turn, the capacity of plants to tolerate potential consequences caused by the extracted/accumulated metals decides the effectiveness and success of phytoremediation system. Chelation is among the potential mechanisms that largely govern metal-tolerance in plant cells by maintaining low concentrations of free metals in cytoplasm. Metal-chelation can be performed by compounds of both thiol origin (such as GSH, glutathione; PCs, phytochelatins; MTs, metallothioneins) and non-thiol origin (such as histidine, nicotianamine, organic acids). This paper presents an appraisal of recent reports on both thiol and non-thiol compounds in an effort to shed light on the significance of these compounds in plant-metal tolerance, as well as to provide scientific clues for the advancement of metal-phytoextraction strategies.

Phytostabilization potential of Jatropha curcas L. in polymetallic acid mine tailings.

Greenhouse pot experiments were conducted to determine the growth response, metal tolerance, and phytostabilization potential of Jatropha curcas L The plants were grown on different degrees of multi-metal contaminated acid mine soils (T0, control; T1, moderately and T2, highly contaminated soils) with or without limestone amendments. The order of metal accumulation in J. curcas was roots>stems>leaves. The higher tolerance index (>90%) with no phytotoxic symptoms and growth reduction in T1 showed that this plant has the ability to tolerate polymetallic acid mine tailings. Further, various enzymatic and non-enzymatic antioxidants also actively involved in metal defense mechanism in J. curcas. On the other hand, to alleviate the predominant phytoavailable toxic metals such as Al, Cu, and Pb, different rates (0.1, 0.25, 0.50, and 1%) of limestone amendments were added in both T1 and T2 soils. The growth performance of J. curcas was improved due to the increase in soil pH and decrease in phytoavailable soil A1 (95%), Zn (approximately 75%), and Cu (approximately 65%) contents at 0.50% of lime addition. Based on the inherent tolerance ability of J. curcas in existing adverse environmental conditions without liming, it could be used as a suitable candidate for phytostabilization in acid mine tailings.

Interaction of cadmium and zinc on accumulation and sub-cellular distribution in leaves of hyperaccumulator Potentilla griffithii.

Potentilla griffithii Hook is a newly found hyperaccumulator plant capable of high tolerance and accumulation of Zn and Cd. We investigated the interactive effects between Cd and Zn on accumulation and vacuolar sequestration in P. griffithii. Stimulatory effect of growth was noted at 0.2 mM Cd and 1.25 and 2.5 mM Zn tested. Accumulation of Zn and Cd in roots, petioles and leaves were increased significantly with addition of these metals individually. However, the Zn supplement decreased root Cd accumulation but increased the concentration of Cd in petioles and leaves. The results from sub-cellular distribution showed that up to 94% and 70% of the total Zn and Cd in the leaves were present in the protoplasts, and more than 90% Cd and Zn in the protoplasts were localized in the vacuoles. Nearly, 88% and 85% of total Cd and Zn were extracted in the cell sap of the leaves suggesting that most of the Cd and Zn in the leaves were available in soluble form. The present results indicate that Zn supplement significantly enhanced the petiole accumulation of Cd and further vacuolar sequestration plays an important role in tolerance, detoxification and hyperaccumulation of these metals in P. griffithii.

The response of high and low polyamine-producing cell lines to aluminum and calcium stress.

The diamine putrescine (Put) has been shown to accumulate in tree leaves in response to high Al and low Ca in the soil, leading to the suggestion that this response may provide a physiological advantage to leaf cells under conditions of Al stress. The increase in Put is reversed by Ca supplementation in the soil. Using two cell lines of poplar (Populus nigra x maximowiczii), one with constitutively high Put (resulting from transgenic expression of a mouse ornithine decarboxylase--called HP cells) and the other with low Put (control cells), we investigated the effects of reduced Ca (0.2-0.8 mM vs. 4 mM) and treatment with 0.1 mM Al on several biochemical parameters of cells. We found that in the presence of reduced Ca concentration, the HP cells were at a disadvantage as compared to control cells in that they showed greater reduction in mitochondrial activity and a reduction in the yield of cell mass. Upon addition of Al to the medium, the HP cells, however, showed a reversal of low-Ca effects. We conclude that due to increased ROS production in the HP cells, their tolerance to low Ca is compromised. Contrary to the expectation of deleterious effects, the HP cells showed an apparent advantage in the presence of Al in the medium, which could have come from reduced uptake of Al, enhanced extrusion of Al following its accumulation, and perhaps a reduction in Put catabolism as a result of a reduction in its biosynthesis.